A. Field of the Invention
This invention relates generally to the field of analytical instruments for conducting biological sample testing. More particularly, the invention relates to a card detection device used in an analytical instrument to detect the presence of a card as the card is moved card through the instrument.
B. Description of Related Art
A variety of test sample cards are described in the patent literature which have a well or reaction site for receiving a fluid sample containing a microbiological agent, such as a microorganism, and a reagent. Several representative patents include Meyer et al., U.S. Pat. No. 4,318,994, Charles et al., U.S. Pat. No. 4,116,775; Fadler et al., U.S. Pat. No. 4,038,151, O'Bear et al., U.S. Pat. No. 5,609,828 and Charles et al., U.S. Pat. No. 4,118,280. These patents describe a test sample card having a plurality of wells arranged in the test sample card body. The reagent is typically loaded in the wells of the card during the completion of manufacture of the card. The reagent typically comprises a growth medium for the microbiological agent. It is known to load a different reagent in each of the wells of the card in order to perform identification testing of a fluid sample containing an unknown microbiological agent or organism. It is also known to use the cards to test the microbiological agent for susceptibility to antibiotics by loading various antibiotic reagents into the wells.
In the sample testing system described in the Charles et al '280 patent, after the well of the test sample card has been loaded with the fluid sample, the card is incubated for a period of time (typically between 2 and 18 hours at a temperature of approximately 35.degree. C.) so as to promote a reaction between the microorganism and the reagent, i.e., growth of the microorganism. During the incubation period, the well is periodically subject to optical analysis by a transmittance light source and a detector which are positioned on opposite sides of the well, or by alternate detection methods. If the growth medium or reagent is specifically suited for or "matches up" with the particular microorganism in the fluid sample, the population of the microorganism increases substantially, or some other predetermined reaction, i.e., chemical reaction, takes place, which results in the well turning cloudy and thus having a change in light transmission characteristics. The detector determines the amount of light that is transmitted from the source through the well. By comparing the transmittance measurement over a period of time, typically several hours at least, with an initial transmittance measurement, it is possible to determine whether in fact the reagent and microbiological agent are matched by virtue of the change in transmittance measurement reaching a threshold value, such as 25 or 30 percent. The change in light transmission characteristics therefore can be used to indicate the presence of a specific microorganism in the well for purposes of identification or determine its sensitivity to antibiotics. Identification and susceptibility may also be detected by other optical measurements such as fluorescence where a fluorescent agent is provided in the growth medium. These methods could also be useful for other temperature dependent kinetic assays such as analytical chemistry or nucleic acid probe based testing.
Due to the fact that the test sample cards described above are often used in clinical and industrial laboratories to identify unknown microorganisms in human test samples, or food test samples generally for the purpose of diagnosing or detecting disease causing microorganisms, the art has recognized that the time required for incubation of the test sample card should be kept to a minimum, so that results can be obtained as quickly as possible. Further, since multiple cards are typically incubated simultaneously in an analytical instrument, it is important that the incubation station be designed such that all of the cards be maintained at the same incubation conditions for relatively long periods of time. Additionally, the card should be incubated in a manner in which all parts of the card are maintained at the same temperature and air flow, so as to provide an even temperature and oxygen distribution to all the wells in the test sample card.
The incubation and reading station described in the above-reference Charles et al. '280 patent meets these requirements fairly well, and has been commercialized with success by the assignee of the present invention. However, the station is essentially a manual station, in that it requires the test sample cards to be externally prepared and manually loaded into station. As such, this design is not optimal for use in a fully automated analytical instrument in which the cards are prepared (i.e., loaded with the test sample) and introduced into and removed from the incubation station automatically. Achieving the above-described performance criteria for an incubation station in a fully automated analytical instrument is a particularly difficult task.
The present inventors have developed an incubation station for an analytical instrument that is a part of a fully automated system. The station is described in detail herein. In the process of developing the station, they have made several discoveries. First, the physical structures or framework that hold the cards in place in the incubation station can adversely effect the even flow and distribution of warm air introduced into the incubation station. Second, this disruption in the distribution of warm air, caused by the carousel structures can lead to localized pools of warmer and cooler air or variances in air flow across the card, which can adversely affect the even or uniform incubation of the card and prolong the amount of time required to incubate the card sufficient to achieve a test result. Third, the inventors have also discovered that the temperature and/or airflow at various locations in the incubation station are different relative to card position by an amount that is also sufficient to adversely affect the time needed to obtain test results. The inventors have also discovered that the solution to these problems has been to incorporate novel features in the construction of the incubation station that optimizes the flow of warm air over the test sample cards, and that accounts for or is in accord with the geometry and spatial distribution of wells in the card and structures that hold the cards in place in the incubation station.
As a result of these findings, the inventors have created a design of a incubation station for a test sample card that is not only particularly well suited for use in an automated analytical instrument, in that it is a fully automatic system, but have also designed the incubation station to achieve a substantially constant temperature distribution and air flow around the test sample cards for as long a period of time as required to incubate the test sample card.
Analytical instruments frequently use card or similar types of structures for purposes of holding a sample to be tested. In another aspect of the invention, an automatic sample testing machine is described which includes a device which detects the cards that are carried by a cassette through the instrument, and thus can keep track of the number of cards that are being processed.